At present, solid-liquid separation in environmental protection and chemical industry requires high precision, and the processed materials are often difficult to separate. The filtration equipment is required to have a simple structure, accurate and convenient operation, the output of the filtrate as clear as possible, a short muddy time in the initial filtration stage, and sufficient mechanical strength and rigidity. And it is required to carefully consider the chemical composition of materials from the aspects of economic efficiency and quality control and require the entire process to be completed in a sealed system. The bag filter is a new type of filter that can meet the above requirements and is suitable for solid-liquid separation of difficult-to-filter suspensions. In order to explore its characteristics, we conducted an experimental study of the bag filter.
Structure and working principle
Filtering on the surface of the filter medium. In the initial stage, the fresh filter medium makes the filtration efficiency higher. The coarse particles of the suspension first bridge the surface of the filter medium to form a filter cake layer, while the smaller particles flow away with the filtrate (generally filtered The medium itself cannot play the role of precision filtration), the filtrate at this time is not clear (contains many tiny particles) as the filtration time increases, the filter layer thickens, the tiny particles are captured in the filter cake layer, and the filtrate is clarified The degree of filtration continues to increase, and the filtration resistance continues to increase (in the filtration process, the resistance of the filter medium can be considered as a constant, but the resistance of the filter cake layer increases with the increase of the thickness of the filter cake). The filtration time increases to a certain extent, and the tiny particles and gels block the flow channel of the filter medium to filter the liquid, causing the filtration rate of the filter medium to decrease, until the flow channel is completely blocked.
The bag filter is composed of two main parts: the housing of the filter and the filter bag. The filtration process is carried out on the surface of the filter medium to clean the filter bag using a very convenient backflushing and backwashing process. The working principle of the novel filter press device is: the filter slurry (suspension) is pumped into the pressure vessel and filtered through the filter bag. Since the diameter of the filter bag is larger than the cage frame during filtration, the filter bag is close to the cage frame during filtration. The intercepted solid particles are attached to the surface of the filter bag to form a filter cake, and the filtrate filtered through the filter bag is discharged out of the shell. When the filter cake layer adhering to the surface of the filter bag reaches the optimal thickness in operation, the filtration is stopped, the residual liquid is discharged, and the filter bag is blown back with compressed air to unload the residue. When back blowing, the filter bag expands and returns to its original diameter, and the filter cake on the outer wall of the filter bag cracks into small pieces that are not connected to each other. The reverse blowing makes the filter bag constantly vibrate. After the filter cake is unloaded, the filter bag is reversed with washing water to regenerate the filter bag. The bag filter applies this back-blowing and backwashing technology, which can keep the filter bag in a clean state and always filter in a better state. Therefore, the bag filter is particularly suitable for the separation of difficult-to-filter suspensions containing more tiny particles and jelly.
